Process for utilizing a water stream in a hydrolysis reaction to form ethanol

ABSTRACT

In one embodiment, the invention is to a process for producing a water stream comprising the steps of hydrogenating acetic acid to form a crude ethanol product and separating at least a portion of the crude ethanol product in at least one column of a plurality of columns into a distillate comprising ethanol and a residue comprising the water stream. The water stream preferably is essentially free of organic impurities other than acetic acid and ethanol.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/542,309, filed Jul. 5, 2012, which is a continuation of U.S.application Ser. No. 12/852,297, filed Aug. 6, 2010, which issued asU.S. Pat. No. 8,222,466 and which claims priority to U.S. ProvisionalApplication No. 61/300,815, filed on Feb. 2, 2010, U.S. ProvisionalApplication No. 61/332,696, filed on May 7, 2010; U.S. ProvisionalApplication No. 61/332,699, filed on May 7, 2010, U.S. ProvisionalApplication No. 61/332,728, filed on May 7, 2010, and U.S. ProvisionalApplication No. 61/346,344, filed on May 19, 2010, the entireties ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to processes for producing awater stream from ethanol production and, in particular, to processesfor producing a water stream that is essentially free of organicimpurities from a crude ethanol product.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from petrochemicalfeed stocks, such as oil, natural gas, or coal; from feed stockintermediates, such as syngas; or from starchy materials or cellulosematerials, such as corn and sugar cane. Conventional methods forproducing ethanol from petrochemical feed stocks, as well as fromcellulose materials, include the acid-catalyzed hydration of ethylene,methanol homologation, direct alcohol synthesis, and Fischer-Tropschsynthesis. Instability in petrochemical feed stock prices contributes tofluctuations in the cost of conventionally produced ethanol, making theneed for alternative sources of ethanol production all the greater whenfeed stock prices rise. Starchy materials, as well as cellulosematerial, are often converted to ethanol by fermentation. However,fermentation is typically used for consumer production of ethanol. Inaddition, fermentation of starchy or cellulose materials competes withfood sources and places restraints on the amount of ethanol that can beproduced for industrial use.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. During the reduction of alkanoicacid, e.g., acetic acid, other compounds are formed with ethanol or areformed in side reactions. In addition, water may be formed in an equalmolar ratio with ethanol during the hydrogenation of acetic acid. Theseimpurities limit the production and recovery of ethanol from suchreaction mixtures. In addition, the impurities may be present in one ormore purge streams. When impurities are present in water purge streams,the water purge stream must be treated, either chemically orbiologically, to remove the impurities before the purge stream may bedisposed. The further treatment adds costs and decreases the overallefficiency of producing ethanol.

Therefore, a need remains for an ethanol production process wherein theseparation portion of the process produces a purified water stream that,as formed, contains little, if any, impurities. This water stream wouldnot require further processing in order to be subsequently used orresponsibly disposed.

SUMMARY OF THE INVENTION

In one embodiment, the invention is to a process for producing a waterstream. The process comprises the step of hydrogenating an acetic acidfeed stream to form a crude ethanol product. The crude ethanol productpreferably comprises ethanol, water, ethyl acetate, and acetic acid. Theprocess further comprises the step of separating at least a portion ofthe crude ethanol product in at least one column of a plurality ofcolumns into a distillate comprising ethanol and a residue comprisingthe water stream.

In another embodiment, the invention is to a process for producing awater stream. The process comprises the step of providing a crudeethanol product comprising ethanol, water, ethyl acetate, and aceticacid. The process further comprises the step of separating at least aportion of the crude ethanol product in at least one column of aplurality of columns into a distillate comprising ethanol and a residuecomprising the water stream.

The separating step, in some embodiments, further comprises the steps ofseparating at least a portion of the crude ethanol product in a firstcolumn of the plurality of columns into a first distillate comprisingethanol, water and ethyl acetate, and a first residue comprising aceticacid; separating at least a portion of the first distillate in a secondcolumn of the plurality of columns into a second distillate comprisingethyl acetate and a second residue comprising ethanol and water; andseparating at least a portion of the second residue in a third column ofthe plurality of columns into a third distillate comprising ethanol anda third residue comprising the water stream.

In preferred embodiments, the at least one column has a base temperatureranging from 70 to 110° C. In other embodiment, the base temperature ofthe at least one column is at least 102° C.

Preferably, the resultant water stream is essentially free of organicimpurities other than acetic acid and ethanol, In one embodiment, theresultant water stream comprises at least 97 wt. % water; less than 0.5wt. % acetic acid; less than 0.005 wt. % ethanol; and less than 0.001wt. % ethyl acetate. In other embodiments, the water stream water streamhas a pH ranging from 2.99 to 3.35.

In one embodiment, the process comprises the step of hydrogenatingacetic acid in a reactor in the presence of a catalyst to form a crudeethanol product. The crude ethanol product may comprise ethanol, water,ethyl acetate, and/or acetic acid. The process may further comprise thestep of separating at least a portion of the crude ethanol product,optionally in a first column, into a first distillate and a firstresidue. The first distillate may comprise ethanol, water and ethylacetate and the first residue may comprise acetic acid. The process mayfurther comprise the step of separating at least a portion of the firstdistillate, optionally in a second column, into a second distillate anda second residue. The second distillate may comprise ethyl acetate andthe second residue may comprise ethanol and water. The process mayfurther comprise the step of separating at least a portion of the secondresidue, optionally in a third column, into a third distillate and athird residue. The third distillate may comprise ethanol and the thirdresidue may comprise at least 97 wt. % water; less than 0.5 wt. % aceticacid; less than 0.005 wt. % ethanol; and less than 0.001 wt. % ethylacetate. The process may further comprise the step of hydrolyzing atleast a portion of the second distillate with at least a portion of thethird residue.

In one embodiment, the invention relates to process for producing awater stream. The process comprises the step of providing the crudeethanol product comprising ethanol, water, acetic acid, and ethylacetate, e.g., hydrogenating a feed stream comprising acetic acid toform a crude ethanol product comprising ethanol, water, ethyl acetate,and acetic acid. The process may further comprise the step of separatingat least a portion of the crude ethanol product to form at least oneethanol stream and a water stream. The at least one ethanol stream maycomprise ethanol and ethyl acetate and the water stream may comprise atleast 97 wt. % water; less than 0.5 wt. % acetic acid; less than 0.005wt. % ethanol; and less than 0.001 wt. % ethyl acetate. The process mayfurther comprise the step of hydrolyzing at least a portion of the ethylacetate in the at least one ethanol stream with at least a portion ofthe water stream to form a hydrolyzed stream comprising ethanol.

BRIEF DESCRIPTION OF DRAWINGS

The invention is described in detail below with reference to theappended drawings, wherein like numerals designate similar parts.

FIG. 1 is a schematic diagram of a hydrogenation system for ethanolproduction in accordance with one embodiment of the present invention.

FIG. 2 is a schematic diagram of a hydrogenation system for ethanolproduction in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally relates to the separation of a crudeethanol product to form a water stream that is essentially free oforganic impurities other than acetic acid and ethanol. For purposes ofthe present invention organic impurities may include ethyl acetate,acetaldehyde, acetone, acetal, and mixtures thereof. In one embodiment,the amount of organic impurities other than acetic acid and ethanol maybe less than 10 wppm, e.g., less than 5 wppm or less than 1 wppm.

The crude ethanol product is preferably formed via the hydrogenation ofacetic acid in an acetic acid feed stream. The hydrogenation ispreferably performed in the presence of a catalyst. The hydrogenation ofacetic acid to form ethanol and water may be represented by thefollowing reaction:

In theoretical embodiments where ethanol and water are the only productsof the hydrogenation reaction, the crude ethanol product comprises 71.9wt. % ethanol and 28.1 wt. % water. However, not all of the acetic acidfed to the hydrogenation reactor is typically converted to ethanol.Subsequent reactions of ethanol, such as esterification, may form otherbyproducts such as ethyl acetate. Crude ethanol products are describedin Tables 1 and 2, below.

The present invention, in one embodiment, relates to processes forproducing a water stream from a crude ethanol mixture that comprises theimpurities discussed above. In one embodiment, the crude ethanol productmay be separated using at least one, e.g., at least two or at leastthree, column(s) of a plurality of columns. Preferably, the crudeethanol product or a derivative stream thereof is fed to a distillationcolumn, which yields a distillate comprising ethanol and a residuecomprising the water stream.

As one example, the water stream comprises at least 97 wt. % water,e.g., at least 98 wt. % or at least 99 wt. %. The water stream mayfurther comprise less than 0.5 wt. % acetic acid, e.g., less than 0.1wt. % or less than 0.05 wt. %. The water stream may also comprises lessthan 0.005 wt. % ethanol, e.g., less than 0.002 wt. % or less than 0.001wt. %. Preferably, the water stream has a pH ranging from 2.99 to 3.35,e.g., from 3.05 to 3.29 or from 3.10 to 3.23.

1. Hydrogenation Process

Suitable hydrogenation catalysts include catalysts comprising a firstmetal and optionally one or more of a second metal, a third metal oradditional metals, optionally on a catalyst support. The first andoptional second and third metals may be selected from Group IB, IIB,IIIB, IVB, VB, VIB, VIIB, VIII transitional metals, a lanthanide metal,an actinide metal or a metal selected from any of Groups IIIA, IVA, VA,and VIA. Preferred metal combinations for some exemplary catalystcompositions include platinum/tin, platinum/ruthenium, platinum/rhenium,palladium/ruthenium, palladium/rhenium, cobalt/palladium,cobalt/platinum, cobalt/chromium, cobalt/ruthenium, silver/palladium,copper/palladium, nickel/palladium, gold/palladium, ruthenium/rhenium,and ruthenium/iron. Exemplary catalysts are further described in U.S.Pat. No. 7,608,744 and US Publication No. 2010/0029995, the entiretiesof which are incorporated herein by reference. Additional catalysts aredescribed in US Pub. No. 2010/0197485, filed on Feb. 2, 2010, theentirety of which is incorporated herein by reference.

In one exemplary embodiment, the catalyst comprises a first metalselected from the group consisting of copper, iron, cobalt, nickel,ruthenium, rhodium, palladium, osmium, iridium, platinum, titanium,zinc, chromium, rhenium, molybdenum, and tungsten. Preferably, the firstmetal is selected from the group consisting of platinum, palladium,cobalt, nickel, and ruthenium. More preferably, the first metal isselected from platinum and palladium. When the first metal comprisesplatinum, it is preferred that the catalyst comprises platinum in anamount less than 5 wt. %, e.g., less than 3 wt. % or less than 1 wt. %,due to the high demand for platinum.

As indicated above, the catalyst optionally further comprises a secondmetal, which typically would function as a promoter. If present, thesecond metal preferably is selected from the group consisting of copper,molybdenum, tin, chromium, iron, cobalt, vanadium, tungsten, palladium,platinum, lanthanum, cerium, manganese, ruthenium, rhenium, gold, andnickel. More preferably, the second metal is selected from the groupconsisting of copper, tin, cobalt, rhenium, and nickel. More preferably,the second metal is selected from tin and rhenium.

If the catalyst includes two or more metals, e.g., a first metal and asecond metal, the first metal optionally is present in the catalyst inan amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt. %, or from 0.1to 3 wt. %. The second metal preferably is present in an amount from 0.1and 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to 5 wt. %. Forcatalysts comprising two or more metals, the two or more metals may bealloyed with one another or may comprise a non-alloyed metal solution ormixture.

The preferred metal ratios may vary depending on the metals used in thecatalyst. In some exemplary embodiments, the mole ratio of the firstmetal to the second metal is from 10:1 to 1:10, e.g., from 4:1 to 1:4,from 2:1 to 1:2, from 1.5:1 to 1:1.5 or from 1.1:1 to 1:1.1.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from the first and second metals.In preferred aspects, the third metal is selected from the groupconsisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin,and rhenium. More preferably, the third metal is selected from cobalt,palladium, and ruthenium. When present, the total weight of the thirdmetal preferably is from 0.05 and 4 wt. %, e.g., from 0.1 to 3 wt. %, orfrom 0.1 to 2 wt. %.

In addition to one or more metals, the exemplary catalysts furthercomprise a support or a modified support, meaning a support thatincludes a support material and a support modifier, which adjusts theacidity of the support material. The total weight of the support ormodified support, based on the total weight of the catalyst, preferablyis from 75 wt. % to 99.9 wt. %, e.g., from 78 wt. % to 97 wt. %, or from80 wt. % to 95 wt. %. In preferred embodiments that use a modifiedsupport, the support modifier is present in an amount from 0.1 wt. % to50 wt. %, e.g., from 0.2 wt. % to 25 wt. %, from 0.5 wt. % to 15 wt. %,or from 1 wt. % to 8 wt. %, based on the total weight of the catalyst.

Suitable support materials may include, for example, stable metaloxide-based supports or ceramic-based supports. Preferred supportsinclude silicaceous supports, such as silica, silica/alumina, a GroupIIA silicate such as calcium metasilicate, pyrogenic silica, high puritysilica, and mixtures thereof. Other supports may include, but are notlimited to, iron oxide, alumina, titania, zirconia, magnesium oxide,carbon, graphite, high surface area graphitized carbon, activatedcarbons, and mixtures thereof.

In the production of ethanol, the catalyst support may be modified witha support modifier. Preferably, the support modifier is a basic modifierthat has a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metaloxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. Inaddition to oxides and metasilicates, other types of modifiers includingnitrates, nitrites, acetates, and lactates may be used. Preferably, thesupport modifier is selected from the group consisting of oxides andmetasilicates of any of sodium, potassium, magnesium, calcium, scandium,yttrium, and zinc, as well as mixtures of any of the foregoing.Preferably, the support modifier is a calcium silicate, and morepreferably calcium metasilicate (CaSiO₃). If the support modifiercomprises calcium metasilicate, it is preferred that at least a portionof the calcium metasilicate is in crystalline form.

A preferred silica support material is SS61138 High Surface Area (HSA)Silica Catalyst Carrier from Saint Gobain NorPro. The Saint-GobainNorPro SS61138 silica contains approximately 95 wt. % high surface areasilica; a surface area of about 250 m²/g; a median pore diameter ofabout 12 nm; an average pore volume of about 1.0 cm³/g as measured bymercury intrusion porosimetry and a packing density of about 0.352 g/cm³(22 lb/ft³).

A preferred silica/alumina support material is KA-160 (Sud Chemie)silica spheres having a nominal diameter of about 5 mm, a density ofabout 0.562 g/ml, in absorptivity of about 0.583 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g.

As will be appreciated by those of ordinary skill in the art, supportmaterials are selected such that the catalyst system is suitably active,selective and robust under the process conditions employed for theformation of ethanol.

The metals of the catalysts may be dispersed throughout the support,coated on the outer surface of the support (egg shell) or decorated onthe surface of the support.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. No. 7,608,744, US Publication Nos. 2010/0029995, and 2010/0197485,referred to above, the entireties of which are incorporated herein byreference.

Some embodiments of the process of hydrogenating acetic acid to formethanol according to one embodiment of the invention may include avariety of configurations using a fixed bed reactor or a fluidized bedreactor, as one of skill in the art will readily appreciate. In manyembodiments of the present invention, an “adiabatic” reactor can beused; that is, there is little or no need for internal plumbing throughthe reaction zone to add or remove heat. In other embodiments, radialflow reactor or reactors may be employed, or a series of reactors may beemployed with or without heat exchange, quenching, or introduction ofadditional feed material. Alternatively, a shell and tube reactorprovided with a heat transfer medium may be used. In many cases, thereaction zone may be housed in a single vessel or in a series of vesselswith heat exchangers therebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phaseor vapor phase. Preferably, the reaction is carried out in the vaporphase under the following conditions. The reaction temperature may rangefrom 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to300° C., or from 250° C. to 300° C. The pressure may range from 10 KPato 3000 KPa (about 1.5 to 435 psi), e.g., from 50 KPa to 2300 KPa, orfrom 100 KPa to 1500 KPa. The reactants may be fed to the reactor at agas hourly space velocity (GHSV) of greater than 500 hr⁻¹, e.g., greaterthan 1000 hr⁻¹, greater than 2500 or even greater than 5000 hr⁻¹. Interms of ranges the GHSV may range from 50 hr⁻¹ to 50,000 hr⁻¹, e.g.,from 500 hr⁻¹ to 30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹, or from1000 hr⁻¹ to 6500 hr⁻¹.

The hydrogenation optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 12:1 to 1:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is greater than2:1, e.g., greater than 4:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,of from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to30 seconds.

The raw materials, acetic acid and hydrogen, used in connection with theprocess of this invention may be derived from any suitable sourceincluding natural gas, petroleum, coal, biomass, and so forth. Asexamples, acetic acid may be produced via methanol carbonylation,acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, andanaerobic fermentation. As petroleum and natural gas prices fluctuatebecoming either more or less expensive, methods for producing aceticacid and intermediates such as methanol and carbon monoxide fromalternate carbon sources have drawn increasing interest. In particular,when petroleum is relatively expensive compared to natural gas, it maybecome advantageous to produce acetic acid from synthesis gas (“syngas”) that is derived from any available carbon source. U.S. Pat. No.6,232,352, the disclosure of which is incorporated herein by reference,for example, teaches a method of retrofitting a methanol plant for themanufacture of acetic acid. By retrofitting a methanol plant, the largecapital costs associated with CO generation for a new acetic acid plantare significantly reduced or largely eliminated. All or part of the syngas is diverted from the methanol synthesis loop and supplied to aseparator unit to recover CO and hydrogen, which are then used toproduce acetic acid. In addition to acetic acid, such a process can alsobe used to make hydrogen which may be utilized in connection with thisinvention.

Methanol carbonylation processes suitable for production of acetic acidare described in U.S. Pat. Nos. 7,208,624, 7,115,772, 7,005,541,6,657,078, 6,627,770, 6,143,930, 5,599,976, 5,144,068, 5,026,908,5,001,259, and 4,994,608, the disclosure of which are incorporatedherein by reference in their entireties. Optionally, the production ofethanol may be integrated with such methanol carbonylation processes.

U.S. Pat. No. RE 35,377 also incorporated herein by reference in itsentirety, provides a method for the production of methanol by conversionof carbonaceous materials such as oil, coal, natural gas and biomassmaterials. The process includes hydrogasification of solid and/or liquidcarbonaceous materials to obtain a process gas which is steam pyrolizedwith additional natural gas to form synthesis gas. The syn gas isconverted to methanol which may be carbonylated to acetic acid. Themethod likewise produces hydrogen which may be used in connection withthis invention as noted above. U.S. Pat. No. 5,821,111, which disclosesa process for converting waste biomass through gasification intosynthesis gas as well as U.S. Pat. No. 6,685,754, the disclosures ofwhich are incorporated herein by reference in their entireties.

In one optional embodiment, the acetic acid fed to the hydrogenationreaction may also comprise other carboxylic acids and anhydrides, aswell as acetaldehyde and acetone. Preferably, a suitable acetic acidfeed stream comprises one or more of the compounds selected from thegroup consisting of acetic acid, acetic anhydride, acetaldehyde, andmixtures thereof. These other compounds may also be hydrogenated in theprocesses of the present invention. In some embodiments, the present ofcarboxylic acids, such as propanoic acid or its anhydride, may bebeneficial in producing propanol.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the ethanol synthesis reaction zones of thepresent invention without the need for condensing the acetic acid andlight ends or removing water, saving overall processing costs.

The acetic acid may be vaporized at the reaction temperature, followingwhich the vaporized acetic acid can be fed along with hydrogen in anundiluted state or diluted with a relatively inert carrier gas, such asnitrogen, argon, helium, carbon dioxide and the like. For reactions runin the vapor phase, the temperature should be controlled in the systemsuch that it does not fall below the dew point of acetic acid. In oneembodiment the acetic acid may be vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is transferred to the vapor state by passinghydrogen, recycle gas, another suitable gas, or mixtures thereof throughthe acetic acid at a temperature below the boiling point of acetic acid,thereby humidifying the carrier gas with acetic acid vapors, followed byheating the mixed vapors up to the reactor inlet temperature.Preferably, the acetic acid is transferred to the vapor by passinghydrogen and/or recycle gas through the acetic acid at a temperature ator below 125° C., followed by heating of the combined gaseous stream tothe reactor inlet temperature.

In particular, the hydrogenation of acetic acid may achieve favorableconversion of acetic acid and favorable selectivity and productivity toethanol. For purposes of the present invention, the term “conversion”refers to the amount of acetic acid in the feed that is converted to acompound other than acetic acid. Conversion is expressed as a molepercentage based on acetic acid in the feed. The conversion may be atleast 10%, e.g., at least 20%, at least 40%, at least 50%, at least 60%,at least 70% or at least 80%. Although catalysts that have highconversions are desirable, such as at least 80% or at least 90%, in someembodiments a low conversion may be acceptable at high selectivity forethanol. It is, of course, well understood that in many cases, it ispossible to compensate for conversion by appropriate recycle streams oruse of larger reactors, but it is more difficult to compensate for poorselectivity.

Selectivity is expressed as a mole percent based on converted aceticacid. It should be understood that each compound converted from aceticacid has an independent selectivity and that selectivity is independentfrom conversion. For example, if 50 mole % of the converted acetic acidis converted to ethanol, we refer to the ethanol selectivity as 50%.Preferably, the catalyst selectivity to ethoxylates is at least 60%,e.g., at least 70%, or at least 80%. As used herein, the term“ethoxylates” refers specifically to the compounds ethanol,acetaldehyde, and ethyl acetate. Preferably, the selectivity to ethanolis at least 80%, e.g., at least 85% or at least 88%. Preferredembodiments of the hydrogenation process also have low selectivity toundesirable products, such as methane, ethane, and carbon dioxide. Theselectivity to these undesirable products preferably is less than 4%,e.g., less than 2% or less than 1%. More preferably, these undesirableproducts are not detectable. Formation of alkanes may be low, andideally less than 2%, less than 1%, or less than 0.5% of the acetic acidpassed over the catalyst is converted to alkanes, which have littlevalue other than as fuel.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. A productivity of at least200 grams of ethanol per kilogram catalyst per hour, e.g., at least 400grams of ethanol per kilogram catalyst per hour or at least 600 grams ofethanol per kilogram catalyst per hour, is preferred. In terms ofranges, the productivity preferably is from 200 to 3,000 grams ofethanol per kilogram catalyst per hour, e.g., from 400 to 2,500 perkilogram catalyst per hour or from 600 to 2,000 per kilogram catalystper hour.

In various embodiments, the crude ethanol product produced by thehydrogenation process, before any subsequent processing, such aspurification and separation, will typically comprise unreacted aceticacid, ethanol, and water. As used herein, the term “crude ethanolproduct” refers to any composition comprising from 5 to 70 wt. % ethanoland from 5 to 35 wt. % water. In some exemplary embodiments, the crudeethanol product comprises ethanol in an amount from 5 wt. % to 70 wt. %,e.g., from 10 wt. % to 60 wt. %, or from 15 wt. % to 50 wt. %, based onthe total weight of the crude ethanol product. Preferably, the crudeethanol product contains at least 10 wt. % ethanol, at least 15 wt. %ethanol or at least 20 wt. % ethanol. The crude ethanol producttypically may further comprise unreacted acetic acid, depending onconversion, for example, in an amount of less than 90 wt. %, e.g., lessthan 80 wt. % or less than 70 wt. %. In terms of ranges, the unreactedacetic acid is preferably from 0 to 90 wt. %, e.g., from 5 to 80 wt. %,from 15 to 70 wt. %, from 20 to 70 wt. % or from 25 to 65 wt. %. Aswater is formed in the reaction process, water will generally be presentin the crude ethanol product, for example, in amounts ranging from 5 to35 wt. %, e.g., from 10 to 30 wt. % or from 10 to 26 wt. %. Ethylacetate may also be produced during the hydrogenation of acetic acid orthrough side reactions and may be present, for example, in amountsranging from 0 to 20 wt. %, e.g., from 0 to 15 wt. %, from 1 to 12 wt. %or from 3 to 10 wt. %. Acetaldehyde may also be produced through sidereactions and may be present, for example, in amounts ranging from 0 to10 wt. %, e.g., from 0 to 3 wt. %, from 0.1 to 3 wt. % or from 0.2 to 2wt. %. Other components, such as, for example, esters, ethers,aldehydes, ketones, alkanes, and carbon dioxide, if detectable,collectively may be present in amounts less than 10 wt. %, e.g., lessthan 6 wt. % or less than 4 wt. %. In terms of ranges, other componentsmay be present in an amount from 0.1 to 10 wt. %, e.g., from 0.1 to 6wt. %, or from 0.1 to 4 wt. %. Exemplary embodiments of crude ethanolcompositional ranges are provided in Table 1.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 70 10 to 60  15to 50 25 to 50 Acetic Acid 0 to 90 5 to 80 15 to 70 20 to 70 Water 5 to35 5 to 30 10 to 30 10 to 26 Ethyl Acetate 0 to 20 0 to 15  1 to 12  3to 10 Acetaldehyde 0 to 10 0 to 3  0.1 to 3  0.2 to 2  Others 0.1 to 10 0.1 to 6   0.1 to 4  —

2. Separation of Crude Ethanol Product

FIGS. 1 and 2 show hydrogenation systems 100 suitable for thehydrogenation of acetic acid and the separation of ethanol from thecrude reaction mixture according to some embodiments of the invention.In FIG. 1, system 100 comprises reaction zone 101 and distillation zone102. Reaction zone 101 comprises reactor 103, hydrogen feed line 104 andacetic acid feed line 105. Distillation zone 102 comprises flasher 106,first column 107, second column 108, and third column 109. FIG. 2further comprises a fourth column 123 in distillation zone 102 forfurther the overheads from the second column 108.

In FIGS. 1 and 2, hydrogen and acetic acid are fed to a vaporizer 110via lines 104 and 105, respectively, to create a vapor feed stream inline 111 that is directed to reactor 103. In one embodiment (not shown),lines 104 and 105 may be combined and jointly fed to the vaporizer 110,e.g., in one stream containing both hydrogen and acetic acid. Thetemperature of the vapor feed stream in line 111 is preferably from 100°C. to 350° C., e.g., from 120° C. to 310° C. or from 150° C. to 300° C.Any feed that is not vaporized is removed from vaporizer 110, as shownin FIG. 1, and may be recycled thereto. In addition, although FIG. 1shows line 111 being directed to the top of reactor 103, line 111 may,be directed to the side, upper portion, or bottom of reactor 103.Further modifications and additional components to reaction zone 101 aredescribed below.

Reactor 103 contains the catalyst that is used in the hydrogenation ofthe acetic acid. In one embodiment, one or more guard beds (not shown)may be used to protect the catalyst from poisons or undesirableimpurities contained in the feed or return/recycle streams. The guardbeds may be employed in the vapor or liquid streams. Suitable guard bedmaterials are known in the art and include, for example, carbon, silica,alumina, ceramic, and/or resins. In one aspect, the guard bed media isfunctionalized to trap particular species such as sulfur or halogens.During the hydrogenation process, a crude ethanol product is withdrawn,preferably continuously, from reactor 103 via line 112. The crudeethanol product may be condensed and fed to flasher 106, which, in turn,provides a vapor stream and a liquid stream. The flasher 106 in oneembodiment preferably operates at a temperature of from 50° C. to 500°C., e.g., from 70° C. to 400° C. or from 100° C. to 350° C. In oneembodiment, the pressure of flasher 106 preferably is from 50 KPa to2000 KPa, e.g., from 75 KPa to 1500 KPa or from 100 to 1000 KPa. In onepreferred embodiment the temperature and pressure of the flasher issimilar to the temperature and pressure of the reactor 103.

The vapor stream exiting the flasher 106 may comprise hydrogen andhydrocarbons, which may be purged and/or returned to reaction zone 101via line 113. As shown in FIG. 1, the returned portion of the vaporstream passes through compressor 114 and is combined with hydrogen feed104 and co-fed to vaporizer 110.

The liquid from flasher 106 is withdrawn and pumped as a feedcomposition via line 115 to the side of first column 107, also referredto as the acid separation column. The contents of line 115 typicallywill be substantially similar to the product obtained directly from thereactor, and may, in fact, also be characterized as a crude ethanolproduct. However, the feed composition in line 115 preferably hassubstantially no hydrogen, carbon dioxide, methane or ethane, which areremoved by flasher 106. Exemplary compositions of line 115 are providedin Table 2. It should be understood that liquid line 115 may containother components, not listed, such as components in the feed.

TABLE 2 FEED COMPOSITION Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Ethanol 5 to 70    10 to 60 15 to 50 Acetic Acid <90    5 to 80 15 to 70Water 5 to 35    5 to 30 10 to 30 Ethyl Acetate <20  0.001 to 15  1 to12 Acetaldehyde <10 0.001 to 3 0.1 to 3  Acetal <5 0.001 to 2 0.005 to1    Acetone <5  0.0005 to 0.05 0.001 to 0.03  Other Esters <5 <0.005<0.001 Other Ethers <5 <0.005 <0.001 Other Alcohols <5 <0.005 <0.001

The amounts indicated as less than (<) in the tables throughout thepresent application are preferably not present and if present may bepresent in trace amounts or in amounts not greater than 0.0001 wt. %.

The “other esters” in Table 2 may include, but are not limited to, ethylpropionate, methyl acetate, isopropyl acetate, n-propyl acetate, n-butylacetate or mixtures thereof. The “other ethers” in Table 2 may include,but are not limited to, diethyl ether, methyl ethyl ether, isobutylethyl ether or mixtures thereof. The “other alcohols” in Table 2 mayinclude, but are not limited to, methanol, isopropanol, n-propanol,n-butanol or mixtures thereof. In one embodiment, the feed composition,e.g., line 115, may comprise propanol, e.g., isopropanol and/orn-propanol, in an amount from 0.001 to 0.1 wt. %, from 0.001 to 0.05 wt.% or from 0.001 to 0.03 wt. %. In should be understood that these othercomponents may be carried through in any of the distillate or residuestreams described herein and will not be further described herein,unless indicated otherwise.

When the content of acetic acid in line 115 is less than 5 wt. %, theacid separation column 107 may be skipped and line 115 may be introduceddirectly to second column 108, also referred to herein as a light endscolumn.

In the embodiment shown in FIG. 1, line 115 is introduced in the lowerpart of first column 107, e.g., lower half or lower third. In firstcolumn 107, unreacted acetic acid, a portion of the water, and otherheavy components, if present, are removed from the composition in line115 and are withdrawn, preferably continuously, as residue. Preferably,residue from first column 107 comprises substantially all of the aceticacid from the crude ethanol product or liquid fed to the first column.Some or all of the residue may be returned and/or recycled back toreaction zone 101 via line 116. Recycling the acetic acid in line 116 tothe vaporizer 110 may reduce the amount of heavies that need to bepurged from vaporizer 110. Reducing the amount of heavies to be purgedmay improve efficiencies of the process while reducing byproducts.

First column 107 also forms an overhead distillate, which is withdrawnin line 117. The distillate, in one embodiment, may be condensed andrefluxed, for example, at a ratio of from 10:1 to 1:10, e.g., from 3:1to 1:3 or from 1:2 to 2:1.

Any of columns 107, 108, 109, or 123 may comprise any distillationcolumn capable of separation and/or purification. The columns preferablycomprise tray columns having from 1 to 150 trays, e.g., from 10 to 100,from 20 to 95 trays or from 30 to 75 trays. The trays may be sievetrays, fixed valve trays, movable valve trays, or any other suitabledesign known in the art. In other embodiments, a packed column may beused. For packed columns, structured packing or random packing may beemployed. The trays or packing may be arranged in one continuous columnor they may be arranged in two or more columns such that the vapor fromthe first section enters the second section while the liquid from thesecond section enters the first section, etc.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in FIGS. 1 and 2. As shown inFIGS. 1 and 2, heat may be supplied to the base of each column or to acirculating bottom stream through a heat exchanger or reboiler. Othertypes of reboilers, such as internal reboilers, may also be used in someembodiments. The heat that is provided to reboilers may be derived fromany heat generated during the process that is integrated with thereboilers or from an external source such as another heat generatingchemical process or a boiler. Although one reactor and flasher are shownin FIGS. 1 and 2, additional reactors, flashers, condensers, heatingelements, and other components may be used in embodiments of the presentinvention.

As will be recognized by those skilled in the art, various condensers,pumps, compressors, reboilers, drums, valves, connectors, separationvessels, etc., normally employed in carrying out chemical processes mayalso be combined and employed in the processes of the present invention.

The temperatures and pressures employed in any of the columns may vary.As a practical matter, pressures from 10 KPa to 3000 KPa will generallybe employed in these zones although in some embodiments subatmosphericpressures may be employed as well as superatmospheric pressures.Temperatures within the various zones will normally range between theboiling points of the composition removed as the distillate and thecomposition removed as the residue. It will be recognized by thoseskilled in the art that the temperature at a given location in anoperating distillation column is dependent on the composition of thematerial at that location and the pressure of column. In addition, feedrates may vary depending on the size of the production process and, ifdescribed, may be generically referred to in terms of feed weightratios.

When column 107 is operated under standard atmospheric pressure, thetemperature of the residue exiting in line 116 from column 107preferably is from 95° C. to 120° C., e.g., from 105° C. to 117° C. orfrom 110° C. to 115° C. The temperature of the distillate exiting inline 117 from column 107 preferably is from 70° C. to 110° C., e.g.,from 75° C. to 95° C. or from 80° C. to 90° C. Column 107 may operate atatmospheric pressure. In other embodiments, the pressure of first column107 may range from 0.1 KPa to 510 KPa, e.g., from 1 KPa to 475 KPa orfrom 1 KPa to 375 KPa. Exemplary components of the distillate andresidue compositions for first column 107 are provided in Table 3 below.It should also be understood that the distillate and residue may alsocontain other components, not listed, such as components in the feed.For convenience, the distillate and residue of the first column may alsobe referred to as the “first distillate” or “first residue.” Thedistillates or residues of the other columns may also be referred towith similar numeric modifiers (second, third, etc.) in order todistinguish them from one another, but such modifiers should not beconstrued as requiring any particular separation order.

TABLE 3 FIRST COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethanol 20 to 75 30 to 70 40 to 65 Water 10 to 40 15 to 35 20to 35 Acetic Acid <2 0.001 to 0.5  0.01 to 0.2  Ethyl Acetate <60 5.0 to40  10 to 30 Acetaldehyde <10 0.001 to 5    0.01 to 4   Acetal <0.1 <0.1<0.05 Acetone <0.05 0.001 to 0.03   0.01 to 0.025 Residue Acetic Acid 60 to 100 70 to 95 85 to 92 Water <30  1 to 20  1 to 15 Ethanol <1 <0.9<0.07

As shown in Table 3, without being bound by theory, it has surprisinglyand unexpectedly been discovered that when any amount of acetal isdetected in the feed that is introduced to the acid separation column(first column 107), the acetal appears to decompose in the column suchthat less or even no detectable amounts are present in the distillateand/or residue.

Depending on the reaction conditions, the crude ethanol product exitingreactor 103 in line 112 may comprise ethanol, acetic acid (unconverted),ethyl acetate, and water. After exiting reactor 103, a non-catalyzedequilibrium reaction may occur between the components contained in thecrude ethanol product until it is added to flasher 106 and/or firstcolumn 107. This equilibrium reaction tends to drive the crude ethanolproduct to an equilibrium between ethanol/acetic acid and ethylacetate/water, as shown below.

EtOH+HOAc⇄EtOAc+H₂O

In the event the crude ethanol product is temporarily stored, e.g., in aholding tank, prior to being directed to distillation zone 102, extendedresidence times may be encountered. Generally, the longer the residencetime between reaction zone 101 and distillation zone 102, the greaterthe formation of ethyl acetate. For example, when the residence timebetween reaction zone 101 and distillation zone 102 is greater than 5days, significantly more ethyl acetate may form at the expense ofethanol. Thus, shorter residence times between reaction zone 101 anddistillation zone 102 are generally preferred in order to maximize theamount of ethanol formed. In one embodiment, a holding tank (not shown),is included between the reaction zone 101 and distillation zone 102 fortemporarily storing the liquid component from line 115 for up to 5 days,e.g., up to 1 day, or up to 1 hour. In a preferred embodiment no tank isincluded and the condensed liquids are fed directly to the firstdistillation column 107. In addition, the rate at which thenon-catalyzed reaction occurs may increase as the temperature of thecrude ethanol product, e.g., in line 115, increases. These reactionrates may be particularly problematic at temperatures exceeding 30° C.,e.g., exceeding 40° C. or exceeding 50° C. Thus, in one embodiment, thetemperature of liquid components in line 115 or in the optional holdingtank is maintained at a temperature less than 40° C., e.g., less than30° C. or less than 20° C. One or more cooling devices may be used toreduce the temperature of the liquid in line 115.

As discussed above, a holding tank (not shown) may be included betweenthe reaction zone 101 and distillation zone 102 for temporarily storingthe liquid component from line 115, for example from 1 to 24 hours,optionally at a temperature of about 21° C., and corresponding to anethyl acetate formation of from 0.01 wt. % to 1.0 wt. % respectively. Inaddition, the rate at which the non-catalyzed reaction occurs mayincrease as the temperature of the crude ethanol product is increased.For example, as the temperature of the crude ethanol product in line 115increases from 4° C. to 21° C., the rate of ethyl acetate formation mayincrease from about 0.01 wt. % per hour to about 0.005 wt. % per hour.Thus, in one embodiment, the temperature of liquid components in line115 or in the optional holding tank is maintained at a temperature lessthan 21° C., e.g., less than 4° C. or less than −10° C.

In addition, it has now been discovered that the above-describedequilibrium reaction may also favor ethanol formation in the top regionof first column 107.

The distillate, e.g., overhead stream, of column 107 optionally iscondensed and refluxed as shown in FIG. 1, preferably, at a reflux ratioof 5:1 to 10:1. The distillate in line 117 preferably comprises ethanol,ethyl acetate, and water, along with other impurities, which may bedifficult to separate due to the formation of binary and tertiaryazeotropes.

The first distillate in line 117 is introduced to the second column 108,also referred to as the “light ends column,” preferably in the middlepart of column 108, e.g., middle half or middle third. As one example,when a 25 tray column is utilized in a column without water extraction,line 117 is introduced at tray 17. In one embodiment, the second column108 may be an extractive distillation column. In such embodiments, anextraction agent, such as water, may be added to second column 108. Ifthe extraction agent comprises water, it may be obtained from anexternal source or from an internal return/recycle line from one or moreof the other columns. For example, the extraction agent may be at leasta portion of the purified water stream from the third column. In oneembodiment, at least a portion of the purified water in line 121 isrecycled to second column 108, as indicated by line 121′. The molarratio of the water in the extraction agent to the ethanol in the feed tothe second column is preferably at least 0.5:1, e.g., at least 1:1 or atleast 3:1. In terms of ranges, preferred molar ratios may range from0.5:1 to 8:1, e.g., from 1:1 to 7:1 or from 2:1 to 6.5:1. Higher molarratios may be used but with diminishing returns in terms of theadditional ethyl acetate in the second distillate and decreased ethanolconcentrations in the second column distillate.

Second column 108 may be a tray column or packed column. In oneembodiment, second column 108 is a tray column having from 5 to 70trays, e.g., from 15 to 50 trays or from 20 to 45 trays.

Although the temperature and pressure of second column 108 may vary,when at atmospheric pressure the temperature of the second residueexiting in line 118 from second column 108 preferably is from 60° C. to90° C., e.g., from 70° C. to 90° C. or from 80° C. to 90° C. Thetemperature of the second distillate exiting in line 120 from secondcolumn 108 preferably is from 50° C. to 90° C., e.g., from 60° C. to 80°C. or from 60° C. to 70° C. Column 108 may operate at atmosphericpressure. In other embodiments, the pressure of second column 108 may befrom 0.1 KPa to 510 KPa, e.g., from 1 KPa to 475 KPa or from 1 KPa to375 KPa. Exemplary components of the second distillate and residuecompositions for second column 108 are provided in Table 4 below. Itshould also be understood that the distillate and residue may alsocontain other components, not listed, such as components in the feed.

TABLE 4 SECOND COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethyl Acetate 10 to 90 25 to 90 50 to 90 Acetaldehyde  1 to25  1 to 15 1 to 8 Water  1 to 25  1 to 20  4 to 16 Ethanol <30 0.001 to15   0.01 to 5   Acetal <5 0.001 to 2    0.01 to 1   Residue Water 30 to70 30 to 60 30 to 50 Ethanol 20 to 75 30 to 70 40 to 70 Ethyl Acetate <30.001 to 2    0.001 to 0.5  Acetic Acid <0.5 0.001 to 0.3  0.001 to 0.2 

The weight ratio of ethanol in the second residue to second distillatepreferably is at least 3:1, e.g., at least 6:1, at least 8:1, at least10:1 or at least 15:1. The weight ratio of ethyl acetate in the secondresidue to second distillate preferably is less than 0.4:1, e.g., lessthan 0.2:1 or less than 0.1:1. In embodiments that use an extractivecolumn with water as an extraction agent as the second column 108, theweight ratio of ethyl acetate in the second residue to ethyl acetate inthe second distillate approaches zero.

As shown, the second residue from the bottom of second column 108, whichcomprises ethanol and water, is fed via line 118 to third column 109.Column 109 may also be referred to as a “product column.” Morepreferably, the second residue in line 118 is introduced in the lowerpart of third column 109, e.g., lower half or lower third. Third column109 recovers ethanol, which preferably is substantially pure other thanthe azeotropic water content, as the distillate in line 119. Thedistillate of third column 109 preferably is refluxed as shown in FIG.1, for example, at a reflux ratio of from 1:10 to 10:1, e.g., from 1:3to 3:1 or from 1:2 to 2:1.

Third column 109 is preferably a tray column as described above andpreferably operates at atmospheric pressure. The temperature of thethird distillate exiting in line 119 from third column 109 preferably isfrom 60° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C. to95° C. The temperature of the third residue, e.g. the water stream,exiting third column 109 preferably is from 70° C. to 110° C., e.g.,from 95° C. to 110° C. or from 100° C. to 105° C., when the column isoperated at atmospheric pressure. In terms of lower limits, thetemperature of the third residue exiting third column 109 is at least102° C., e.g., at least 105° C. or at least 110° C.

Without being bound by theory, the water stream of the present inventioncomprises few, if any, impurities, the water stream may be disposedwithout the need for further processing. Thus, the conventionalnecessity for additional processing to remove impurities isadvantageously minimized or eliminated. Beneficially, this lack ofimpurities may allow for disposal or reuse of the water stream atminimal costs.

The inventive water stream may be suitable for many uses. The uses forthe water stream, in some cases, may be dependent upon the location ofthe facility at which the water stream is produced and the state orlocal government regulations that may apply thereto. For example, theinventive water stream may be suitable for use in industrialapplications. As one example, the water stream may be recycled to theprocess and used in portions of the reaction zone or the separation zonewhere a water stream is needed. In one embodiment, the water stream maybe used as an extraction agent in a distillation column, e.g. a secondcolumn, as discussed above. In another embodiment, the water stream maybe used in hydrolysis reactions or in reactive distillation columns. Inone embodiment, a portion of the third residue may be used to hydrolyzeany other stream, such as one or more streams comprising ethyl acetate.The water stream may also be utilized as a scrubber solvent, e.g., for avent scrubber. Preferably, the water stream maybe utilized in theprocesses of the present invention. In other embodiments, the waterstream maybe utilized in an independent process. As another option, thewater stream may be used to maintain process equipment, e.g., to wash orclear tanks and towers. In a preferred embodiment, the water stream isused as cooling water. In this case, the water stream may be(biologically) treated to prevent algae growth. In other embodiments,the water stream may be used in agricultural applications. These usesare merely exemplary uses and this listing is not exclusive.

Exemplary components of the distillate composition and water stream forthird column 109 are provided in Table 5 below. It should also beunderstood that the distillate may also contain other components, notlisted, such as components in the feed.

TABLE 5 THIRD COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Ethanol 75 to 96 80 to 96 85 to 96 Water <12 1 to 9 3 to 8Acetic Acid <1 0.001 to 0.1  0.005 to 0.01  Ethyl Acetate <5 0.001 to4    0.01 to 3   Water Stream Water  97 to 100  98 to 100  99 to 100Ethanol <0.005 <0.002  <0.001 Ethyl Acetate <0.001 <0.0005 notdetectable Acetic Acid <0.5 <0.1   <0.05  Organic Impurities <0.001<0.0005 not detectable

Any of the compounds that are carried through the distillation processfrom the feed or crude reaction product generally remain in the thirddistillate in amounts of less 0.1 wt. %, based on the total weight ofthe third distillate composition, e.g., less than 0.05 wt. % or lessthan 0.02 wt. %. In one embodiment, one or more side streams may removeimpurities from any of the columns 107, 108 and/or 109 in the system100. Preferably at least one side stream is used to remove impuritiesfrom the third column 109. The impurities may be purged and/or retainedwithin the system 100.

The third distillate in line 119 may be further purified to form ananhydrous ethanol product stream, i.e., “finished anhydrous ethanol,”using one or more additional separation systems, such as, for example,distillation columns (e.g., a finishing column) or mole sieves.

Returning to second column 108, the second distillate preferably isrefluxed as shown in FIG. 1, for example, at a reflux ratio of from 1:10to 10:1, e.g., from 1:5 to 5:1 or from 1:3 to 3:1. In one embodiment,the ester feed stream comprises the all or a portion of the seconddistillate in line 120.

In another embodiment, as shown in FIG. 2, the second distillate is fedvia line 120 to fourth column 123, also referred to as the “acetaldehyderemoval column.” In fourth column 123 the second distillate is separatedinto a fourth distillate, which comprises acetaldehyde, in line 124. Thefourth distillate preferably is refluxed at a reflux ratio of from 1:20to 20:1, e.g., from 1:15 to 15:1 or from 1:10 to 10:1, and a portion ofthe fourth distillate is returned to the reaction zone 101. For example,the fourth distillate may be combined with the acetic acid feed, addedto the vaporizer 110, or added directly to the reactor 103. As shown,the fourth distillate is co-fed with the acetic acid in feed line 105 tovaporizer 110. Without being bound by theory, since acetaldehyde may behydrogenated to form ethanol, the recycling of a stream that containsacetaldehyde to the reaction zone increases the yield of ethanol anddecreases byproduct and waste generation. In another embodiment (notshown in the figure), the acetaldehyde may be collected and utilized,with or without further purification, to make useful products includingbut not limited to n-butanol, 1,3-butanediol, and/or crotonaldehyde andderivatives.

The fourth residue of fourth column 123 in line 125 primarily comprisesethyl acetate and water and is highly suitable for use as an ester feedstream. In one preferred embodiment, the acetaldehyde is removed fromthe second distillate in fourth column 123 such that no detectableamount of acetaldehyde is present in the residue of column 123.

Fourth column 123 is preferably a tray column as described above andpreferably operates above atmospheric pressure. In one embodiment, thepressure is from 120 KPa to 5,000 KPa, e.g., from 200 KPa to 4,500 KPa,or from 400 KPa to 3,000 KPa. In a preferred embodiment the fourthcolumn 123 may operate at a pressure that is higher than the pressure ofthe other columns.

The temperature of the fourth distillate exiting in line 124 from fourthcolumn 123 preferably is from 60° C. to 110° C., e.g., from 70° C. to100° C. or from 75° C. to 95° C. The temperature of the residue exitingfrom fourth column 125 preferably is from 70° C. to 115° C., e.g., from80° C. to 110° C. or from 85° C. to 110° C. Exemplary components of thedistillate and residue compositions for fourth column 109 are providedin Table 6 below. It should also be understood that the distillate andresidue may also contain other components, not listed, such ascomponents in the feed.

TABLE 6 FOURTH COLUMN Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Distillate Acetaldehyde 2 to 80    2 to 50 5 to 40 Ethyl Acetate <90  30 to 80 40 to 75  Ethanol <30 0.001 to 25 0.01 to 20   Water <250.001 to 20 0.01 to 15   Residue Ethyl Acetate 40 to 100    50 to 100 60to 100 Ethanol <40 0.001 to 30 0 to 15 Water <25 0.001 to 20 2 to 15Acetaldehyde <1  0.001 to 0.5 Not detectable Acetal <3 0.001 to 2  0.01to 1   

The finished ethanol composition obtained by the processes of thepresent invention preferably comprises from 75 to 96 wt. % ethanol,e.g., from 80 to 96 wt. % or from 85 to 96 wt. % ethanol, based on thetotal weight of the finished ethanol composition. Exemplary finishedethanol compositional ranges are provided below in Table 7.

TABLE 7 FINISHED ETHANOL COMPOSITIONS Component Conc. (wt. %) Conc. (wt.%) Conc. (wt. %) Ethanol 75 to 96 80 to 96 85 to 96 Water <12 1 to 9 3to 8 Acetic Acid <1 <0.1 <0.01 Ethyl Acetate <2 <0.5 <0.05 Acetal <0.05<0.01 <0.005 Acetone <0.05 <0.01 <0.005 Isopropanol <0.5 <0.1 <0.05n-propanol <0.5 <0.1 <0.05

The finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol is from 95 to 1,000 wppm, e.g., from 100 to 700 wppm, or from150 to 500 wppm. In one embodiment, the finished ethanol compositionpreferably is substantially free of acetaldehyde and may comprise lessthan 8 wppm of acetaldehyde, e.g., less than 5 wppm or less than 1 wppm.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingfuels, solvents, chemical feedstocks, pharmaceutical products,cleansers, sanitizers, hydrogenation transport or consumption. In fuelapplications, the finished ethanol composition may be blended withgasoline for motor vehicles such as automobiles, boats and small pistonengine aircrafts. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used a chemical feedstockto make other chemicals such as vinegar, ethyl acrylate, ethyl acetate,ethylene, glycol ethers, ethylamines, aldehydes, and higher alcohols,especially butanol. In the production of ethyl acetate, the finishedethanol composition may be esterified with acetic acid or reacted withpolyvinyl acetate. The finished ethanol composition may be dehydrated toproduce ethylene. Any of known dehydration catalysts can be employed into dehydrate ethanol, such as those described in U.S. Pub. No.20100030002 and 20100030001, the entire contents and disclosures ofwhich are hereby incorporated by reference. A zeolite catalyst, forexample, may be employed as the dehydration catalyst. Preferably, thezeolite has a pore diameter of at least about 0.6 nm, and preferredzeolites include dehydration catalysts selected from the groupconsisting of mordenites, ZSM-5, a zeolite X and a zeolite Y. Zeolite Xis described, for example, in U.S. Pat. No. 2,882,244 and zeolite Y inU.S. Pat. No. 3,130,007, the entireties of which are hereby incorporatedby reference. In order that the invention disclosed herein may be moreefficiently understood, an example is provided below. The followingexamples describe the various distillation processes of the presentinvention.

EXAMPLES Example 1

A crude ethanol product comprising ethanol, acetic acid, water and ethylacetate was produced by reacting a vaporized feed comprising 95.2 wt. %acetic acid and 4.6 wt. % water with hydrogen in the presence of acatalyst comprising 1.6 wt. % platinum and 1 wt. % tin supported on ⅛inch calcium silicate modified silica extrudates at an averagetemperature of 291° C., an outlet pressure of 2,063 KPa. Unreactedhydrogen was recycled back to the inlet of the reactor such that thetotal H₂/acetic acid molar ratio was 5.8 at a GHSV of 3,893 W^(I). Underthese conditions, 42.8% of the acetic acid was converted, and theselectivity to ethanol was 87.1%, selectivity to ethyl acetate was 8.4%,and selectivity to acetaldehyde was 3.5%. The crude ethanol product waspurified using a separation scheme having distillation columns as shownin FIG. 1.

The crude ethanol product was fed to the first column at a feed rate of20 g/min. The composition of the liquid feed is provided in Table 8. Thefirst column was a 2 inch diameter Oldershaw with 50 trays. The columnwas operated at a temperature of 115° C. at atmospheric pressure. Unlessotherwise indicated, a column operating temperature is the temperatureof the liquid in the reboiler and the pressure at the top of the columnis ambient (approximately one atmosphere). The column differentialpressure between the trays in the first column was 7.4 KPa. The firstresidue was withdrawn at a flow rate of 12.4 g/min and returned to thehydrogenation reactor.

The first distillate was condensed and refluxed at a 1:1 ratio at thetop of the first column, and a portion of the distillate was introducedto the second column at a feed rate of 7.6 g/min. The second column is a2 inch diameter Oldershaw design equipped with 25 trays. The secondcolumn was operated at a temperature of 82° C. at atmospheric pressure.The column differential pressure between the trays in the second columnwas 2.6 KPa. The second residue was withdrawn at a flow rate of 5.8g/min. The second distillate was refluxed at a ratio of 4.5:0.5 and theremaining distillate was collected as the ester feed stream foranalysis.

TABLE 8 First Column Second Column Feed Distillate Residue DistillateResidue Component (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) Water 13.824.7 5.6 5.1 30.8 Acetaldehyde nd 1.8 nd 8.3 nd Acetic Acid 55.0 0.0893.8 0.03 0.1 Ethanol 23.4 57.6 0.06 12.4 67.6 Ethyl Acetate 6.5 15.1 nd76.0 nd Acetal 0.7 0.1 nd 0.006 0.03 Acetone nd 0.01 nd 0.03 nd

Example 2

A feed stream having a similar composition as residue from the secondcolumn from Example 1 was collected from several runs and introducedabove the 25 tray to the third column, a 2 inch Oldershaw containing 60trays, at a rate of 10 g/min. The third column was operated at atemperature of 103° C. at standard pressure. The column differentialpressure between the trays in the third column was 6.2 KPa. The thirdresidue, e.g., the water stream, was withdrawn at a flow rate of 2.7g/min. The third distillate was condensed and refluxed at a 3:1 ratio atthe top of the third column. An ethanol composition as shown in Table 9was recovered. The ethanol composition also contained 10 ppm of n-butylacetate.

TABLE 9 Third Column Feed Distillate Residue Component (wt. %) (wt. %)(wt. %) Acetic Acid 0.098 0.001 0.4 Ethanol 65.7 93.8 0.004 Water 35.56.84 98 Ethyl Acetate 1.37 1.8 — Acetal 0.02 0.03 — Isopropanol 0.0040.005 — n-propanol 0.01 0 —

As shown in Table 9, the residue of the third column, e.g., the waterstream, is surprisingly and unexpectedly free of organic impuritiesother than acetic acid and ethanol. As such, the water stream may beeasily disposed of without further processing.

Example 3

A crude ethanol product comprising ethanol, acetic acid, water and ethylacetate was produced by reacting a vaporized feed comprising 96.3 wt. %acetic acid and 4.3 wt. % water with hydrogen in the presence of acatalyst comprising 1.6 wt. % platinum and 1% tin supported on ⅛ inchcalcium silicate modified silica extrudates at an average temperature of290° C., an outlet pressure of 2,049 kPa. Unreacted hydrogen wasrecycled back to the inlet of the reactor such that the total H₂/aceticacid molar ratio was 10.2 at a GHSV of 1,997 hr⁻¹. Under theseconditions, 74.5% of the acetic acid was converted, and the selectivityto ethanol was 87.9%, selectivity to ethyl acetate was 9.5%, andselectivity to acetaldehyde was 1.8%. The crude ethanol product waspurified using a separation scheme having distillation columns as shownin FIG. 1.

The crude ethanol product was fed to the first column at a feed rate of20 g/min. The composition of the liquid feed is provided in Table 10.The first column is a 2 inch diameter Oldershaw with 50 trays. Thecolumn was operated at a temperature of 116° C. at atmospheric pressure.The column differential pressure between the trays in the first columnwas 8.1 KPa. The first residue was withdrawn at a flow rate of 10.7g/min and returned to the hydrogenation reactor.

The first distillate was condensed and refluxed at a 1:1 ratio at thetop of the first column, and a portion of the distillate was introducedto the second column at a feed rate of 9.2 g/min. The second column wasa 2 inch diameter Oldershaw design equipped with 25 trays. The secondcolumn was operated at a temperature of 82° C. at atmospheric pressure.The column differential pressure between the trays in the second columnwas 2.4 KPa. The second residue was withdrawn at a flow rate of 7.1g/min. The second distillate was refluxed at a ratio of 4.5:0.5 and theremaining distillate was collected as the ester feed stream foranalysis.

TABLE 10 First Column Second Column Feed Distillate Residue DistillateResidue Component (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) Water 14.627.2 3.7 3.0 36.2 Acetaldehyde nd 1.5 nd 10.3 nd Acetic Acid 49.1 0.298.2 0.04 0.3 Ethanol 27.6 54.5 0.04 13.3 64.4 Ethyl Acetate 7.9 15.2 nd75.7 1.8 Acetal 0.7 0.1 nd 0.01 0.02 Acetone nd 0.01 nd 0.03 nd

Example 4

A feed stream having a similar composition as residue from the secondcolumn from Example 3 was collected from several runs and introducedabove the 25 tray to the third column, a 2 inch Oldershaw containing 60trays, at a rate of 20 g/min. The third column was operated at atemperature of 103° C. at standard pressure. The column differentialpressure between the trays in the third column was 6.5 KPa. The thirdresidue, e.g., the water stream, was withdrawn at a flow rate of 13.8g/min. The third distillate was condensed and refluxed at a 3:2 ratio atthe top of the third column. An ethanol composition as shown in Table 11was recovered. The ethanol composition also contained 118 ppm ofisopropanol and 122 ppm of n-propanol.

TABLE 11 Third Column Feed Distillate Residue Component (wt. %) (wt. %)(wt. %) Acetic Acid 0.06 0 0.088 Ethanol 25.2 92.5 0.0012 Water 72.6 7.599.9 Ethyl Acetate 0.0007 0.0019 —

As shown in Table 11, the residue of the third column, e.g., the waterstream, is surprisingly and unexpectedly free of organic impuritiesother than acetic acid and ethanol. As such, the water stream may beeasily disposed of without further processing.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In view of the foregoing discussion, relevantknowledge in the art and references discussed above in connection withthe Background and Detailed Description, the disclosures of which areall incorporated herein by reference. In addition, it should beunderstood that aspects of the invention and portions of variousembodiments and various features recited below and/or in the appendedclaims may be combined or interchanged either in whole or in part. Inthe foregoing descriptions of the various embodiments, those embodimentswhich refer to another embodiment may be appropriately combined withother embodiments as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing a water stream, comprising thesteps of: hydrogenating acetic acid in a reactor in the presence of acatalyst to form a crude ethanol product; separating at least a portionof the crude ethanol product in a first column into a first distillatecomprising ethanol, water and ethyl acetate, and a first residuecomprising acetic acid; separating at least a portion of the firstdistillate in a second column into a second distillate comprising ethylacetate and a second residue comprising ethanol and water; separating atleast a portion of the second residue in a third column into a thirddistillate comprising ethanol and a third residue; hydrolyzing at leasta portion of the second distillate with at least a portion of the thirdresidue, wherein the third residue comprises: at least 97 wt. % water;less than 0.5 wt. % acetic acid; less than 0.005 wt. % ethanol; and lessthan 0.001 wt. % ethyl acetate.
 2. The process of claim 1, wherein thecrude ethanol product comprises ethanol, water, ethyl acetate, andacetic acid.
 3. The process of claim 1, wherein at least a portion ofthe third residue is directed to the second column.
 4. The process ofclaim 1, wherein the crude ethanol product comprises ethanol in anamount of from 5 to 70 wt. %, water in an amount of from 5 to 35 wt. %,acetic acid in an amount of from 0 to 90 wt. %, and ethyl acetate in anamount of from 0 to 20 wt. %.
 5. The process of claim 1, furthercomprising: hydrolyzing at least a portion of the first distillate withat least a portion of the third residue.
 6. The process of claim 1,further comprising: separating at least a portion of the seconddistillate in a fourth column into a fourth distillate comprisingacetaldehyde and a fourth residue comprising ethyl acetate.
 7. Theprocess of claim 6, further comprising: hydrolyzing at least a portionof the fourth residue with at least a portion of the third residue. 8.The process of claim 1, wherein the water stream is essentially free oforganic impurities other than acetic acid and ethanol, and wherein theorganic impurities are selected from the group consisting of ethylacetate, acetaldehyde, acetone, acetal and mixtures thereof.
 9. Theprocess of claim 1, wherein the hydrogenating is conducted over acatalyst comprising a combination of metals selected from the groupconsisting of platinum/tin, platinum/ruthenium, platinum/rhenium,palladium/ruthenium, palladium/rhenium, cobalt/palladium,cobalt/platinum, cobalt/chromium, cobalt/ruthenium, silver/palladium,copper/palladium, nickel/palladium, gold/palladium, ruthenium/rhenium,and ruthenium/iron.
 10. The process of claim 1, wherein the water streamhas a pH ranging from 2.99 to 3.35.
 11. A process for producing a waterstream, the process comprising: hydrogenating a feed stream comprisingacetic acid to form a crude ethanol product comprising ethanol, water,ethyl acetate, and acetic acid; separating at least a portion of thecrude ethanol product to form at least one ethanol stream comprisingethanol and ethyl acetate and a water stream comprising: at least 97 wt.% water; less than 0.5 wt. % acetic acid; less than 0.005 wt. % ethanol;and less than 0.001 wt. % ethyl acetate; and hydrolyzing at least aportion of the ethyl acetate in the at least one ethanol stream with atleast a portion of the water stream to form a hydrolyzed streamcomprising ethanol.
 12. The process of claim 11, wherein the separatingstep comprises: separating at least a portion of the crude ethanolproduct to form a first ethanol stream comprising ethanol and ethylacetate and a first acetic acid stream.
 13. The process of claim 12,wherein the hydrolyzing step comprises: hydrolyzing at least a portionof the ethyl acetate in the first ethanol stream with at least a portionof the at least one water stream to form the hydrolyzed stream.
 14. Theprocess of claim 12, wherein the separating step further comprises:separating at least a portion of the first ethanol stream to form asecond ethanol stream comprising ethanol and ethyl acetate and a firstwater stream comprising ethanol and water and a second water streamcomprising: at least 97 wt. % water; less than 0.5 wt. % acetic acid;less than 0.005 wt. % ethanol; and less than 0.001 wt. % ethyl acetate.15. The process of claim 14, wherein the hydrolyzing step comprises:hydrolyzing at least a portion of the ethyl acetate in the secondethanol stream with at least a portion of the second water stream toform the hydrolyzed stream.
 16. The process of claim 14, wherein theseparating step further comprises: separating at least a portion of thefirst water stream to form a third ethanol stream comprising ethanol andethyl acetate and the second water stream; separating at least a portionof the second ethanol stream to form an acetaldehyde stream and a fourthethanol stream comprising ethanol and ethyl acetate.
 17. The process ofclaim 16, wherein the hydrolyzing step comprises: hydrolyzing at least aportion of the ethyl acetate in the fourth ethanol stream with at leasta portion of the second water stream to form the hydrolyzed stream. 18.The process of claim 16, wherein the hydrolyzing step comprises:hydrolyzing at least a portion of the first ethanol stream and at leasta portion of the fourth ethanol stream with at least a portion of thesecond water stream to form the hydrolyzed stream.
 19. A process forpurifying a crude ethanol product, comprising the steps of: providingthe crude ethanol product comprising ethanol, water, acetic acid, andethyl acetate; separating at least a portion of the crude ethanolproduct to form an ethyl acetate-containing stream and at least onewater stream comprising at least 97 wt. % water; less than 0.5 wt. %acetic acid; less than 0.005 wt. % ethanol; and less than 0.001 wt. %ethyl acetate; and hydrolyzing at least a portion of the ethylacetate-containing stream with at least a portion of the water stream toform a hydrolyzed stream comprising ethanol.
 20. The process of claim19, wherein the crude ethanol product comprises ethanol in an amount offrom 5 to 70 wt. %, water in an amount of from 5 to 35 wt. %, aceticacid in an amount of from 0 to 90 wt. %, and ethyl acetate in an amountof from 0 to 20 wt. %.